Cement compositions may be used in a variety of subterranean operations. For example, in subterranean well construction, a pipe string (e.g., casing, liners, expandable tubulars, etc.) may be run into a wellbore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the wellbore and the exterior surface of the pipe string disposed therein. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (i.e., a cement sheath) that may support and position the pipe string in the wellbore and bond the exterior surface of the pipe string to the subterranean formation. Among other things, the cement sheath surrounding the pipe string functions to prevent the migration of fluids in the annulus and to protect the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods to, for example, seal cracks or holes in pipe strings or cement sheaths, seal highly permeable formation zones or fractures, place cement plugs, and the like.
A broad variety of cement compositions have been used in subterranean cementing operations. In some instances, set-delayed cement compositions have been used. Set-delayed cement compositions are characterized by their ability to remain in a pumpable fluid state for at least about one day (e.g., about 7 days, about 2 weeks, about 2 years or more) at room temperature (i.e., about 80° F.) in quiescent storage. When desired for use, the set-delayed cement compositions may be capable of activation whereby reasonable compressive strengths may be developed. For example, a cement set activator may be added to a set-delayed cement composition whereby the composition sets into a hardened mass. Among other things, the set-delayed cement composition may be suitable for use in wellbore applications, for example, where it is desired to prepare the cement composition in advance. This may allow for the cement composition to be stored prior to its use. In addition, this may allow for the cement composition to be prepared at a convenient location before being transported to the job site. Accordingly, capital and operational expenditures may be reduced due to a reduction in the need for on-site bulk storage and mixing equipment. Advantageously, this may be particularly useful for offshore cementing operations where space onboard the vessels may be limited.
While set-delayed cement compositions have been developed before, challenges exist with their successful use in subterranean cementing operations. For example, set-delayed cement compositions prepared with Portland cement may have undesired gelation issues which may limit their use and effectiveness in cementing operations. Other set-delayed compositions that have been developed, for example, those comprising hydrated lime and quartz, may have limited use at lower temperatures as they may not develop sufficient compressive strength when used in subterranean formations having lower bottom hole static temperatures.
The large-scale manufacture of set-delayed cement compositions may present additional challenges. Large batch mixers or transport trucks used during the manufacturing process of the set-delayed cement compositions may contaminate the set-delayed cement compositions with residual cementitious matter from previous manufacturing operations. The cementitious contaminants may reduce the effectiveness of the retarders or activators used with the set-delayed cement compositions. The cementitious contaminants may even render the set-delayed cement compositions unusable. Thorough cleaning of the mixers before transitioning to a new cement composition may be expensive and decrease manufacturing efficiency. Furthermore the use of cleaning agents (e.g., silica sand) may be ineffective.